This study will examine the significance of a specific hypothalamic-pituitary adrenal aix abnormality to both the classification and treatment of depression. Non-schizophrenic untreated patients in need of a tricyclic antidepressant will be given fixed doses of desipramine over a 6-week period while serial dexamethasone suppression tests and desipramine plasma level determinations are obtained. At the outset, a comprehensive interview will allow a variety of alternative clinical subclassifications. Plasma level-response relationships will be determined within clinically and biologically determined depression subtypes. The potential of the dexamethasone suppression test as a predictor of relapse and suicide will also be tested.